Metabolic and behavior responses of lactating goats under heat stress

Highlights

• Heat stress decreases milk production and alters metabolism and behavior.

• Pancreas of heat-stressed goats secretes lower insulin after glucose infusion.

• Lipid tissue of heat-stressed goats is less sensitive to lipolytic signals.

• Heat stress does not affect eating bouts but makes the duration shorter.

• Heat stress increases drinking bouts without affecting the duration of each bout.

Abstract

Heat stress (HS) negatively affects animal performance, but little is known about energetic metabolism and behavior changes in dairy goats under HS conditions. Eight multiparous Murciano-Granadina dairy goats (43.3 ± 1.6 kg BW; 2 ± 0.04 L milk/d; 81 ± 3 days of lactation) were kept in metabolism cages and randomly assigned to two treatments varying in the temperature humidity index (THI). The design was crossover (two 28-d periods), and treatments were: 1) thermal neutral (TN; 15–20C, 40–45% humidity, THI = 59–65), and 2) heat stress (HS, 12 h/d at 37°C and 40%, and 12 h/d at 30°C and 40%, THI = 86 and 77, respectively). Jugular silicon catheters were fitted, and glucose tolerance test (0.25 g/kg BW), insulin tolerance test (4.6 μg/kg BW) and epinephrine challenge (2 μg/kg BW) were conducted. Before and after each metabolite administration, blood samples were collected for the analysis of insulin, glucose, and nonesterified fatty acids (NEFA). Also, behavior variables (position changes, duration of remaining standing, as well as eating and drinking bouts and duration) were observed at day 3 of each period by video cameras. Heat stress reduced (P < 0.01) feed intake (−29%), milk yield (−10%), milk fat (–12%), milk protein (–14%), and milk casein (–13%). Goats in both groups had similar blood NEFA after insulin administration, but NEFA values were greater (P < 0.05) in TN than HS goats after epinephrine infusion. The HS goats secreted lower (P < 0.05) amounts of insulin than TN goats in response to the glucose tolerance test. Additionally, TN and HS goats had similar number of eating bouts, but the duration of each bout was shorter in HS than in TN. Also, HS had greater number of drinking bouts with no differences in drinking bout durations between groups. In conclusion, body lipid tissue of HS goats became more resistant to lipolysis, making them unable to mobilize body fat reserves despite the negative energy balance. In addition, the reduction in feed intake by HS was because of the shorter time of eating bouts, whereas the greater water consumption was related to the increase in drinking bouts.